Canadian and US ENC charts

[rikhall]

Since you are talking about "chart error" and where they got the data for our current charts - I thought these three paragraphs from a paper by a Master’s student in the Ocean Mapping Group in the Department of Geodesy & Geomatics Engineering at The University of New Brunswick might be of interest.

On September 28, 2003, the Canadian Coast Guard Ship (CCGS) Gordon Reid ran aground on an uncharted rock in Estavan Sound, off the western coast of British Columbia. The best scale chart for this area is Canadian Hydrographic Service (CHS) Chart 3724, the data for which was collected in 1923 by leadline survey on an unknown datum, with line spacing of more than 400 metres, and horizontal positioning provided by sextant.

Ideally, the CHS would want to replace this type of “legacy” data with the current standard of high-quality, full-coverage multibeam sonar surveys, using differential GPS for positioning, when printing their charts. Due to limited monetary and time resources, however, this is not a realistic expectation. Of necessity, legacy data that do not meet modern standards will continue to be the basis for many nautical charts. Attention, then, has been focused in the past twenty years or so on presenting the users of hydrographic products, such as paper and electronic charts, with a measure of data quality.

In the past few years, the CHS has made a practice of putting source class diagrams on their nautical charts, a small box in the corner of the chart showing some details of the survey performed in the area depicted on the particular. But this is a slow and expensive process with the CHS’s dwindling resources, and the diagrams found today on charts are of varying quality, or non-existent.

Local knowledge, error on the side of caution and be careful out there.

Rik

[PaulinVictoria]

Indeed, but my point was more when using charts from different countries at the same time. For example, I could have one chart displayed (with one set of depths) and zoom in causing it to change to a different chart thus displaying a chart with different depths indicated.

[brak]

Originally Posted by PaulinVictoria

Indeed, but my point was more when using charts from different countries at the same time. For example, I could have one chart displayed (with one set of depths) and zoom in causing it to change to a different chart thus displaying a chart with different depths indicated.

True, but the difference in depth due to datum change would likely be less than 1' or so.

[PaulinVictoria]

Possibly, I'd have to compare the two alongside each other which I can't do currently, I can see there being quite a difference as there are often a lot of negative depths on US charts.